1. Field of the Invention
The present invention relates to a method for manufacturing a fuel inlet (fuel feed pipe) for feeding fuel such as gas to a fuel tank of a motor vehicle or the like.
2. Description of the Prior Art
Conventionally, as an inlet pipe which constitutes a fuel inlet, an iron pipe having plating applied thereto and further having coating applied to the plating has been used. Also, with respect to the shape of the inlet pipe, one end of the pipe is eccentrically expanded, and a screw structure is formed in the end so that a cap can be attached thereto. Further a breather pipe is connected to an area of the inlet pipe which is lower than the area where the screw structure is formed, so as to discharge air from a tank.
As a method for eccentrically expanding a pipe member, there has been known a method (D1) in which a pipe member is set in a clamping die, a cored bar is inserted into the pipe member so as to coaxially expand the pipe member, and thereafter the pipe member is eccentrically expanded by using another die and another cored bar. Also, there has been known another method (D2) in which a pipe member is eccentrically expanded without a coaxial expansion process.
A fuel inlet is attached to an area which is susceptible to chipping damage due to pebbles or the like bouncing off a moving tire. Consequently, a coating film or a plating film becomes scratched, and sometimes an iron body is exposed, which causes a problem in resistance especially in a place strongly affected by salt. Thus, there has been proposed another method (D3) in which a stainless pipe is used instead of an iron pipe, a breather pipe is welded to the stainless pipe by projection welding, and thereafter cationic electrodeposition coating is applied to the surface.
D1: Japanese Patent Application Publication 2001-276942
D2: Japanese Patent Application Publication Hei 11-239835
D3: Japanese Patent Application Publication 2002-242779
By using a stainless pipe instead of an iron pipe, it is possible to improve the resistance. However, another problem is caused.
Specifically, in the eccentric expansion process, almost no warpage occurs in the case of an iron pipe, while warpage is greater in the case of a stainless pipe because a stainless pipe is obtained by welding a stainless sheet in a state of being curled to a tube shape and the expansion ratio is different between the welding area and the remaining area.
Also, in the case of a stainless pipe, at the end of the expanded portion where the decrease ratio of the sheet thickness is greatest, the work hardening ratio becomes great. Consequently, processing in a subsequent process becomes difficult.
In addition, since projection welding causes damage to the passive layer of the stainless surface, rust occurs in the area where ring projection welding of the breather pipe is conducted as described in D3.
To solve the above-mentioned problems, according to a first aspect of the present invention, there is provided a method for manufacturing a fuel inlet comprising the steps of eccentrically expanding one end of a stainless pipe so as to prepare an inlet pipe, welding a breather pipe to the inlet pipe, and thereafter applying coating, wherein, in the eccentrically expanding step, the stainless pipe is set into a clamping die having an inside diameter which is the same as the outside diameter of an end product, a cored bar for pipe expansion is inserted into the stainless pipe, and force is applied from the inside of the stainless pipe in the direction of the sheet thickness while the outside of the stainless pipe is restrained.
With this, it is possible to reduce warpage in the eccentrically expanding step.
Further, by applying a lubricant to the entire inner surface of the stainless pipe prior to the eccentrically expanding step, it is possible to prevent the oil from being in short supply on the sliding surface, and to omit application of a lubricant in a subsequent process.
Furthermore, by conducting a surface treatment for reducing friction resistance with respect to the inner surface of the clamping die and the outer surface of the cored bar for pipe expansion which are in contact with the stainless pipe, high accuracy of the eccentric expansion can be achieved.
Also, it is possible to provide a cooling means such as a flow path for cooling water in the cored bar. At the time of expanding the pipe, the friction between the cored bar and the pipe material generates heat, and thus the temperature of the cored bar is increased. As a result, the lubricant disappears and the sliding property is deteriorated. However, with the provision of the cooling means, the above-mentioned drawback can be solved.
To solve the above-mentioned problem, according to a second aspect of the present invention, there is provided a method for manufacturing a fuel inlet comprising the steps of eccentrically expanding one end of a stainless pipe so as to prepare an inlet pipe, welding a breather pipe to the inlet pipe, and thereafter applying coating, wherein, after the eccentrically expanding step, the outer end of the expanded portion is cut and removed.
At the beginning of the expanding step, the end of the pipe is expanded only in the direction of the outside diameter and there is no shrinkage generated in the direction of the axis. Thus, the decrease ratio of the sheet thickness is greater in the end of the pipe than in the remaining area at the beginning of the expanding step, and the end of the pipe suffers from a more excessive work hardening. If the hardened portion is left, processing in a subsequent process will become difficult. However, by removing the hardened portion (the outer end of the expanded portion), it is possible to facilitate processing in a subsequent process.
In order to remove the outer end of the expanded portion, it is preferable to cut from the inside diameter side toward the outside diameter side. By doing so, when curl forming is conducted to the inlet pipe, burr is allowed to be located in the inside of the curl, and thus, human hands are protected from directly contacting the burr.
Further, since the burr is also not located in the inside diameter side of the inlet pipe, even if a pipe expanding method having more processes is employed, there is no fear that the burr will be pinched, no damage will occur, and it is also possible to prevent the treated surface of the cored bar from peeling due to the pinching.
To solve the above-mentioned problem, according to a third aspect of the present invention, there is provided a method for manufacturing a fuel inlet comprising the steps of eccentrically expanding one end of a stainless pipe so as to prepare an inlet pipe, welding a breather pipe to the inlet pipe, and thereafter applying coating, wherein said welding step is conducted by using a brazing material mainly comprised of silver in a reducing atmosphere.
In the case of projection welding, even if cationic electrodeposition coating is applied to the welding area to the breather pipe, it is inevitable that rust will occur. However, by employing brazing, it becomes possible to prevent such a problem.
For the brazing welding, it is preferable to conduct degrease-cleaning by using alkali ionized water as a pretreatment, and to conduct flux-removal-cleaning by using acid ionized water as a subsequent treatment.
Also, for the coating step conducted after the welding step, it is preferable to employ cationic electrodeposition coating using a lead-free coating material or other coating (acrylic silicone coating) using a soluble coating material which contains no hexavalent chromium in order to help protect the environment.